Big question After aeons of speculation, science has finally answered the biggest question of all - Does penis size matter? - with a resounding 'yes'.

Australian researchers have found that penis size is just as important as height when it comes to female assessment of male attractiveness, and that bigger is indeed better - to a point.

The results of the study, which asked a group of women to rate the attractiveness of a series of computer-generated images of varied height, body shape and penis size, are published today in the Proceedings of the National Academy of Science .

"We found that flaccid penis size had a significant influence on male attractiveness," the authors write.

"Males with a larger penis were rated as being relatively more attractive.

"Our results directly contradict claims that penis size is unimportant to most females."

The researchers decided to vary not only penis size but also height and body shape to make it less obvious which characteristic was being manipulated in the digital images.

They found an interaction not only between penis size and height, but also penis size and body shape.

"There was an interaction - penis size was more important if you were a tall individual or a V-shaped, more muscular individual," says co-author Professor Michael Jennions from the Australian National University.

However biggest is not necessarily best. At a length of 7.6 centimetres - an under-average penis size according to large-scale survey of Italian men - the proportional increase in attractiveness began to decrease.

The female participants were told the study was investigating male attractiveness but were not told which male traits were being varied in the life-size projected images.

'P' for 'peacock tail'

The study findings support the hypothesis that penis size partly evolved because of female choice when everything was on show before humans wore clothing.

Penis size at the extremes may be a hormonal signal, or is merely an aesthetic quality, much like the peacock's tail, suggests Jennions.

But before you reach for the tape measure, he is quick to point out that preferences for penis-size or other physical attributes don't necessarily affect how we ultimately select our mates.

"When you're talking about a preference as opposed to how people act and what they do in their lives - we may be perfectly happy with the partner we have even if they are not as tall or well-endowed or have as large-a-breasts as we would like."

Jennions says genital evolution is a topic of great interest to biologists because genitalia evolve unusually rapidly. However there is a notable lack of data in humans.

"We thought it's kind of strange that there's so little done on human penis size and it's such a topic of popular conversation," he says.

"There are endless discussions about it but where's the data? So, being scientists, we thought why don't people just use a completely standard objective method that we would use if we were working on crickets or fish or frogs."